This invention relates to an optical identification system including a reader for reading superimposed optical gratings located in a grating plane on a record medium, like a credit card, even though the optical gratings are slightly displaced from the grating plane while being read.
Recent developments in financial systems, credit systems, security systems, and funds transfer systems rely heavily on the use of record media or "credit cards " having magnetic strips or tracks thereon with various data like account number, credit limits, credit status, credit available for use, and the like being recorded magnetically on the stripes. Such systems have to be designed to avoid or minimize the fraudulent use of such credit cards.
One of the ways in which fraudulent use of such credit cards is made is to counterfeit the cards by mass reproduction techniques which "skim" or transfer the data magnetically recorded on a valid card to a fraudulent one.
The problem of trying to prevent the unauthorized duplication of or use of valid credit cards used in financial systems and the like is a very extensive one as evidenced by the variety of different techniques tried to avoid the problem and which are disclosed in the following U.S. Pat. Nos.:
3,604,901 PA1 3,620,590 PA1 3,759,179, PA1 3,790,754, PA1 3,831,008, PA1 3,401,830, PA1 3,644,716 PA1 3,808,404, PA1 3,697,729, PA1 3,691,527. PA1 3,312,955, PA1 3,392,400, PA1 3,523,734, PA1 3,599,147, PA1 3,635,545, PA1 3,656,838, and PA1 3,838,401.
A copending application Ser. No. 588,937, filed on June 20, 1975 and assigned to the same assignee as this application discloses a system for checking on the validity of credit card used in financial systems and the like by using a "credit card" which has first data recorded thereon in the form of optical gratings and second data which is recorded in a magnetic stripe or track on the card. When the card is used in such a system, the first data is read by an optical grating reading means and the second data is read by a conventional magnetic track reader. The first and second data are then compared to determine the validity of the card being used in the system, and a validity signal is issued depending upon whether the card is valid or not. Because the first data is made up of optical gratings which are embedded in the credit card itself, the optical gratings are tamperproof and can not be easily "skimmed" or counterfeited as data which is magnetically recorded on a card can be. Thus a system is disclosed in said copending application which prevents the mass counterfeiting of valid credit cards. The subject matter of said copending application is incorporated by reference herein.
While the system disclosed in said copending application Ser. No. 588,937 works well, certain elements of the system could be improved upon with regard to the reader for reading the first data which is recorded on the credit card in the form of optical gratings. One of the problems with optical grating readers is that the optical gratings being read must lie in a grating plane if light which is diffracted from the optical gratings is to reach the associated photodetectors which are positioned in the reader with reference to the same grating plane. Accordingly, if a record medium or a "credit card" having the diffraction gratings thereon is slightly bowed, or if the card is moved through the reader so that the optical gratings thereon are located slightly out of the associated grating plane, it is possible that erroneous or missed readings will result.
Accordingly, the optical identification system of the present invention includes a reader which obviates the problems mentioned in the previous paragraph in that it can read the optical or diffraction gratings on a record medium or a "credit card" even though the optical gratings are positioned slightly outside of the associated grating plane during the reading process, thereby making the reader more reliable. The reader of the present invention also is capable of reading superimposed optical gratings which feature represents an improvement in the identification system disclosed in said copending application.
Some systems for recording and reading digital information using diffraction gratings are shown in the following U.S. Pat. Nos.:
While these patents show the use of diffraction gratings in systems for recording and reading information, the readers and systems shown herein employ structure which is quite different from that employed in this invention.